LT3750
Capacitor Charger
Controller
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FEATURES
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DESCRIPTIO
The LT®3750 is a flyback converter designed to rapidly
charge large capacitors to a user-adjustable target voltage. A patented boundary mode control scheme* minimizes transition losses and reduces transformer size. The
transformer turns ratio and two external resistors easily
adjust the output voltage.* A low 78mV current sense
accurately limits peak switch current and also helps to
maximize efficiency. With a wide input voltage range, the
LT3750 can operate from a variety of power sources. A
typical application can charge a 100µF capacitor to 300V
in less than 300ms.
Charges Any Size Capacitor
Easily Adjustable Output Voltage
Drives High Current NMOS FETs
Primary-Side Sense—No Output Voltage Divider
Necessary
Wide Input Range: 3V to 24V
Drives Gate to VCC – 2V
Available in 10-Lead MS Package
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APPLICATIO S
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Emergency Warning Beacons
Professional Photoflash Systems
Security/Inventory Control Systems
High Voltage Power Supply
Electric Fences
Detonators
The CHARGE pin gives full control of the LT3750 to the
user. The DONE pin indicates when the capacitor has
reached its programmed value and the part has stopped
charging.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents, including 6518733, 6636021.
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TYPICAL APPLICATIO
300V, 6A Capacitor Charger
T1
1:10
VTRANS
56µF
×2
10µF
D1
VOUT
300V
•
6A Charge Time
+
300
100µF
VCC
10µF
100k
60.4k
VTRANS = 6V
200
43k
DONE
RDCM
LT3750
OFF ON
VTRANS = 18V
250
CHARGE
GATE
M1
VOUT (V)
VCC
12V
VTRANS
RVOUT
•
VTRANS = 12V
150
100
SOURCE
GND
50
RBG
12mΩ
2.49k
100pF
3750 TA01a
0
0
0.1
0.2
0.3
TIME (SECONDS)
0.4
0.5
3750 TA03c
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LT3750
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
VCC, VTRANS, GATE, DONE, CHARGE ...................... 24V
RBG ....................................................................... 1.5V
SOURCE ................................................................... 1V
Current into RDCM Pin ........................................ ±1mA
Current into RVOUT Pin ........................................ ±1mA
Current into DONE Pin ......................................... ±1mA
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
VTRANS
DONE
CHARGE
VCC
GND
10
9
8
7
6
1
2
3
4
5
RBG
RVOUT
RDCM
GATE
SOURCE
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 120°C/ W
ORDER PART NUMBER
LT3750EMS
MS PART MARKING
LTBQD
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VCC = VTRANS = 5V unless otherwise specified.
PARAMETER
CONDITIONS
MIN
●
Minimum VCC
Minimum VTRANS
●
TYP
MAX
2.8
2.5
3
3
UNITS
V
V
VCC Quiescent Current
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0V
1.6
2.5
1
mA
µA
VTRANS Quiescent Current
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0V
140
250
1
µA
µA
CHARGE Pin Current
CHARGE = 24V
CHARGE = 5V
CHARGE = 0V
24
19
1
1.1
µA
µA
µA
V
20
V
µs
CHARGE Pin Enable Voltage
●
CHARGE Pin Disable Voltage
Minimum CHARGE Pin Low Time
●
High→Low→High
VOUT Comparator Trip Voltage
VOUT Comparator Overdrive
Measured RBG Pin
1µs Pulse Width, Measured on RBG Pin
RBG Pin Bias Current
DCM Comparator Trip Voltage
RBG = 1.2V
Measured as VDRAIN – VTRANS, RDCM = 43k (Note 3)
Current Limit Comparator Trip Voltage
DONE Output Signal High
100kΩ to 5V
DONE Output Signal Low
DONE Pin Leakage Current
100kΩ to 5V
DONE = 2.5V
0.87
0.2
●
1.215
●
●
0.6
1.24
30
1.265
V
mV
5
70
36
500
80
nA
mV
68
4.9
78
5
88
mV
V
0.1
0.2
0.2
V
µA
NMOS Minimum On Time
GATE Rise Time
µs
ns
0.6
50
GATE High Voltage
CGATE = 1nF, VCC = 5V
CGATE = 1nF, VCC = 24V
GATE Turn Off Propagation Delay
CGATE = 1nF
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
3
22
3.8
22.6
100
4.5
23.5
V
V
ns
Note 2: The LT3750E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Refer to Block Diagram for VDRAIN definition.
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LT3750
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TYPICAL PERFOR A CE CHARACTERISTICS
VCC Pin Current
VTRANS Pin Current
1.8
VCC = 12V
1.5
40
VCC = 3V
1.4
200
CHARGE PIN CURRENT (µA)
VTRANS PIN CURRENT (µA)
1.6
45
VTRANS = 24V
VCC = 24V
1.7
VCC PIN CURRENT (mA)
CHARGE Pin Current
225
VTRANS = 12V
175
VTRANS = 3V
150
125
–50°C
35
30
25°C
25
20
125°C
15
10
5
1.3
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
100
–50
125
–25
50
25
0
75
TEMPERATURE (°C)
100
3750 G01
0.6
CHARGE PIN DISABLE
0.5
0.4
8
12
16
VCHARGE (V)
24
20
GATE High Voltage
25
VDONE = 5V
RDONE = 100k
VCC = 24V
20
140
GATE PIN VOLTAGE (V)
DONE PIN VOLTAGE (mV)
0.8
CHARGE PIN ENABLE
4
3750 G03
DONE Output Signal Low
160
0.9
CHARGE PIN VOLTAGE (V)
0
3750 G02
CHARGE Pin Enable/Disable
Voltage
0.7
0
125
120
100
15
VCC = 12V
10
VCC = 5V
5
0.3
–25
50
25
75
0
TEMPERATURE (°C)
100
80
–50
125
–25
75
0
25
50
TEMPERATURE (°C)
100
DCM Comparator Trip Voltage
VOUT Comparator Trip Voltage
VOUT COMPARATOR TRIP VOLTAGE (V)
DCM COMPARATOR TRIP VOLTAGE (mV)
1.240
RDCM = 43k
50
1.236
40
1.232
30
1.228
20
10
–50
1.224
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3750 G07
–25
50
25
0
75
TEMPERATURE (°C)
3750 G05
3750 G04
60
0
–50
125
1.220
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3750 G08
125
100
3750 G06
CURRENT LIMIT COMPARATOR TRIP VOLTAGE (mV)
0.2
–50
Current Limit Comparator Trip
Voltage
82
80
78
76
74
72
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3750 G09
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LT3750
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PI FU CTIO S
VTRANS (Pin 1): Transformer Supply Pin. Powers the
primary coil of the transformer as well as internal circuitry
that performs boundary mode detection. Bypass at the pin
with a 1µF to 10µF capacitor. Bypass the primary winding
of the transformer with a large capacitor.
DONE (Pin 2): Open Collector Indication Pin. When target
output voltage is reached, an NPN transistor turns on.
Requires a pull-up resistor or current source. Any fault
conditions such as thermal shutdown or undervoltage
lockout will also turn on the NPN.
CHARGE (Pin 3): Charge Pin. Initiates a new charge cycle
when brought high or discontinues charging and puts part
into shutdown when low. To properly enable the device, a
step input with a minimum ramp rate of 1V/µs is required.
Drive to 1.1V or higher to enable the device; drive below
0.2V to disable the device.
VCC (Pin 4): Input Supply Pin. Bypass locally with a
ceramic capacitor. A 1µF to 10µF ceramic capacitor should
be sufficient for most applications.
GND (Pin 5): Ground Pin. Connect directly to local ground
plane.
SOURCE (Pin 6): Source Pin. Senses NMOS drain current.
Connect NMOS source terminal and current sense resistor
to this pin. The current limit is 78mV/RSENSE.
GATE (Pin 7): Gate Pin. Connect NMOS gate terminal to
this pin. Internal gate driver will drive voltage to within
VCC – 2V during each switching cycle.
RDCM (Pin 8): Discontinuous Mode Sense Pin. Senses
when current in transformer has decayed to zero and initiates a new charge cycle if output voltage target has not
been reached. Place a resistor between this pin and the drain
of the NMOS. A good choice is a 43k, 5% resistor.
RVOUT (Pin 9): Output Voltage VI Converter Pin. Develops
a current proportional to output capacitor voltage. Connect a resistor between this pin and the drain of the NMOS.
RBG (Pin 10): Output Voltage Sense Pin. Senses the
voltage across the RBG resistor, which is proportional to
the current flowing into the RVOUT pin. When voltage
equals 1.24V, charging is disabled and DONE pin goes
low. Connect a resistor (2.5k or less is recommended)
from this pin to GND. A 2.49k, 1% resistor is a good
choice.
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LT3750
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BLOCK DIAGRA
VTRANS
RDONE
2
1
DONE
2.8V
+
VTRANS
VCC
UVLO
D1
T1
1:N
•
VCC
RVOUT
VTRANS
UVLO
2.5V
VTRANS
+
VOUT
–
+
DCM
COMPARATOR
–
+
160°C
–
RVOUT
9
RDCM
8
ONE
SHOT
–
DIE
TEMP
RDCM
+
COUT
•
TSD
+–
VTRANS
36mV
VDRAIN
VCC
S
M1
ENABLE
R
GATE
Q
4
7
M1
Q Q
S R
+
SOURCE
+
VOUT
COMPARATOR
3
CHARGE
–
6
1.24V
CURRENT LIMIT
COMPARATOR
ONE
SHOT
GND
5
10
RBG
–
RSENSE
+
–
78mV
3750 BD
RBG
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LT3750
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OPERATIO
The LT3750 is designed to charge capacitors quickly and
efficiently. Operation can be best understood by referring
to Figures 1 and 2. Operation proceeds in four phases:
1. Start-up, 2. Primary-side charging, 3. Secondary energy transfer, 4. Discontinuous mode sensing.
1. Start-Up
2. Primary Side Charging
When the NMOS on latch is set, the gate driver rapidly
charges the gate pin to VCC – 2V. The external NMOS turns
on forcing VTRANS – VDS(ON) across the primary winding.
Consequently, current in the primary coil rises linearly at
ILPRI
Start-up occurs for approximately 20µs after the charge
pin is raised high. During this phase, a one-shot enables
the master latch and turns on the NMOS. The master latch
will remain in the set state until the target output voltage
is reached or a fault condition resets it.
1:N
VTRANS
+
•
ILPRI
VPRI
•
+
ILSEC
VTRANS – VDS(ON)
LPRI
ILSEC
S2
VOUT + VDIODE
LSEC
IPK
N
+
VSEC
–
–
3750 F01a
S1
VDRAIN
IPK
VPRI
VTRANS – VDS(ON)
–
(1a) Equivalent Circuit During Primary-Side Charging
1:N
VTRANS
+
ILSEC
•
ILPRI
VPRI
•
+
S2
–(VOUT + VDIODE)
N
+
VSEC
VSEC
–
VOUT + VDIODE
–
3750 F01b
S1
VDRAIN
–
(1b) Equivalent Circuit During Secondary Energy
Transfer and Output Detection
1:N
VTRANS
+
ILPRI
VPRI
•
+
VDRAIN
–
ILSEC
•
–N (VTRANS – VDS(ON))
S2
V
+ VDIODE
VTRANS + OUT
N
VDRAIN
+
VTRANS
VSEC
–
3750 F01c
S1
VDS(ON)
VDS(ON)
–
(1c) Equivalent Circuit During Discontinuous Mode Detection
Figure 1. Equivalent Circuits
3750 F02
1.
PRIMARY-SIDE
CHARGING
3.
2.
DISCONTINUOUS
SECONDARY
MODE
ENERGY TRANSFER
DETECTION
AND OUTPUT
DETECTION
Figure 2. Idealized Charging Waveforms
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LT3750
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OPERATIO
a rate (VTRANS – VDS(ON))/LPRI. The input voltage is mirrored on the secondary winding –N • (VTRANS – VDS(ON))
which reverse biases the diode and prevents current flow
in the secondary winding. Thus, energy is stored in the
core of the transformer.
3. Secondary Energy Transfer
When current limit is reached, the current limit comparator resets the NMOS on-latch and the device enters the
third phase of operation, secondary energy transfer. The
energy stored in the transformer core forward biases the
diode and current flows into the output capacitor. During
this time, the output voltage (neglecting the diode drop) is
reflected back to the primary coil. If the target output
voltage is reached, the VOUT comparator resets the master
latch and the DONE pin goes low. Otherwise, the device
enters the next phase of operation.
4. Discontinuous Mode Detection
Once all the current is transferred to the output capacitor,
(VOUT + VDIODE)/N will appear across the primary winding.
A transformer with no energy cannot support a DC voltage,
so, the voltage across the primary will decay to zero. In
other words, the drain of the NMOS will ring down from
VTRANS + (VOUT + VDIODE)/N to VTRANS. When the drain
voltage falls to VTRANS + 36mV, the DCM comparator sets
the NMOS on-latch and a new charge cycle begins. Steps
2-4 continue until the target output voltage is reached.
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Safety Warning
Switching Period
Large capacitors charged to high voltage can deliver a
lethal amount of energy if handled improperly. It is particularly important to observe appropriate safety measures when designing the LT3750 into applications. First,
create a discharge circuit that allows the designer to safely
discharge the output capacitor. Second, adequately space
high voltage nodes from adjacent traces to satisfy printed
circuit board voltage breakdown requirements. High voltage nodes are the drain of the NMOS, the secondary side
of the transformer, and the output.
The LT3750 employs an open-loop control scheme causing the switching period to decrease with output voltage.
Typical switching frequency is between 100kHz to 300kHz.
Figure 3 shows typical switching period in an application
with a 3A peak current.
20
TIME (µs)
16
Transformer Selection
The flyback transformer is critical to proper operation of
the LT3750. It must be designed carefully so that it does
not cause excessive current or voltage on any pin of the
part.
8
4
0
As with all circuits, the LT3750 has finite bandwidth. In
order to give the LT3750 sufficient time to detect the
output voltage, observe the following restrictions on the
primary inductance:
LPRI ≥
12
0
50
100
150
200
VOUT (V)
250
300
3750 F03
Figure 3. Typical Switching Period vs VOUT
Output Diode Selection
VOUT • 1µs
N • IPK
otherwise, the LT3750 may overcharge the output.
Linear Technology has worked with several leading magnetic component manufacturers to produce flyback transformers for use with the LT3750. Table 1 summarizes the
particular transformer characteristics.
When choosing the rectifying diode, ensure its peak
repetitive forward current rating exceeds the peak current (IPK/N) and that the peak repetitive reverse voltage
rating exceeds VOUT + (N)(VTRANS). The average current
through the diode varies during the charge cycle because
the switching period decreases as VOUT increases. The
average current through the diode is greatest when the
Table 1. Recommended Transformers
PART NUMBER
SIZE L × W × H (mm)
MAXIMUM IPRI (A)
LPRI (µH)
TURNS RATIO (PRI:SEC)
DCT15EFD-U44S003
DCT20EFD-U32S003
22.5 × 16.5 × 8.5
30 × 22 × 12
5
10
10
10
1:10
1:10
Sumida
(www.sumida.com)
C8118 Rev P1
C8117 Rev P1
C8119 Rev P1
21 × 14 × 8
23 × 18.6 × 10.8
32.3 × 27 × 14
3
5
10
10
10
10
1:10
1:10
1:10
Midcom
(www.midcom.com)
32050
32051
32052
23.1 × 18 × 9.4
28.7 × 22 × 11.4
28.7 × 22 × 11.4
3
5
10
10
10
10
1:10
1:10
1:10
Coilcraft
(www.coilcraft.com)
DA2032-AL
DA2033-AL
DA2034-AL
17.2 × 22 × 8.9
17.4 × 24.1 × 10.2
20.6 × 30 × 11.3
3
5
10
10
10
10
1:10
1:10
1:10
MANUFACTURER
TDK
(www.tdk.com)
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output capacitor is almost completely charged and is
given by:
IAVG,D =
(
IPK • VTRANS
2 VOUT(PK ) + N • VTRANS
)
The output diode’s continuous forward current rating
must exceed IAVG,D.
At a minimum, the diode must satisfy all the previously
mentioned specifications to guarantee proper operation.
However, to optimize charge time, reverse recovery time
and reverse bias leakage current should be considered.
Excessive diode reverse recovery times can cause appreciable discharging of the output capacitor thereby increasing charge time. Choose a diode with a reverse
recovery time of less than 100ns. Diode leakage current
under high reverse bias bleeds the output capacitor of
charge, also increasing charge time. Choose a diode that
has minimal reverse bias leakage current. Table 2 recommends several output diodes for various output voltages
with adequate reverse recovery time.
Table 2. Recommended Output Diodes
MANUFACTURER
Diodes Inc.
(www.diodes.com)
Philips
(www.semiconductors.
philips.com)
PART
NUMBER
IDC
(A)
PEAK
REPETITIVE
REVERSE
VOLTAGE
(V)
MURS140
MURS160
ES2G
US1M
1
1
2
1
400
600
400
1000
SMB
SMB
SMB
SMA
BYD147
BYD167
1
1
400
500
SOD87
SOD87
can result in improper operation. This most often manifests itself in two ways. The first is when the primary winding current looks distorted instead of triangular. This
substantially reduces the efficiency and increases the
charge time. The second way is when the LT3750 fails to
detect discontinuous mode after the first switching cycle.
Both of these problems are solved by increasing the amount
of capacitive bypassing for the transformer. Choose capacitors that can handle the high RMS ripple currents
common in flyback regulators.
Output Capacitor Selection
For photoflash applications, the output capacitor will be
discharged into a Xenon flash bulb. Only a pulse capacitor
or photoflash capacitor is able to survive such a harsh
event. Igniting a typical Xenon bulb requires approximately 250V to 350V stored on a capacitor on the order of
hundreds of microfarads.
Table 3. Recommended Output Capacitor Vendors
VENDOR
WEBSITE
Rubycon
www.rubycon.com
Cornell Dubilier
www.cornell-dubilier.com
NWL
www.nwl.com
NMOS Selection
PACKAGE
Bypass Capacitor Selection
Use a high quality X5R or X7R dielectric ceramic capacitor
placed close to the LT3750 to locally bypass the VCC and
VTRANS pins. For most applications, a 1µF to 10µF ceramic
capacitor should suffice for VCC and a 1µF to 10µF for the
VTRANS pin.
The high peak currents flowing through the transformer
necessitate a larger (>>10µF) capacitor to bypass the primary winding of the transformer. Inadequate bypassing
Choose an external NMOS with minimal gate charge and
on resistance that satisfies current limit and voltage breakdown requirements. The gate is nominally driven to VCC –
2V during each charge cycle. Ensure that this does not
exceed the maximum gate to source voltage rating of the
NMOS but enhaces the channel enough to minimize the on
resistance. Similarly, the maximum drain-source voltage
rating of the NMOS must exceed VTRANS + VOUT/N or the
magnitude of the leakage inductance spike, whichever is
greater. The maximum instantaneous drain current must
exceed current limit. Because the switching period decreases with output voltage, the average current through
the NMOS is greatest when the output is nearly charged
and is given by:
IAVG,M =
(
IPK • VOUT(PK )
2 VOUT(PK ) + N • VTRANS
)
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Table 4. Recommended NMOS Transisitors
MANUFACTURER
PART NUMBER
ID (A)
VDS(MAX) (V)
VGS(MAX) (V)
RDS(ON) (mΩ)
PACKAGE
Philips Semiconductor
(www.semiconductors.philips.com)
PHM21NQ15T
PHK12NQ10T
PHT6NQ10Y
PSMN038-100K
22.2
11.6
6.5
6.3
150
100
100
100
20
20
20
20
55
28
90
38
HVSON8
SO-8
SOT223
SO-8
IRF7488
IRF7493
IRF6644
6.3
9.3
10.3
80
80
100
20
20
20
29
15
10.7
SO-8
SO-8
DirectFET
International Rectifier
(www.irf.com)
The transistor’s continuous drain current rating must
exceed IAVG,M.
Table 4 lists recommended NMOS transistors.
Setting Current Limit
A sense resistor from the SOURCE pin to GND implements
current limit. The current limit is nominally 78mV/RSENSE.
The average power dissipation rating of the current sense
resistor must exceed:
PRESISTOR ≥
⎞
VOUT(PK )
IPK 2 • RSENSE ⎛
⎜
⎟
3
⎝ VOUT(PK ) + N • VTRANS ⎠
Additionally, there is approximately a 100ns propagation
delay from the time that peak current limit is detected to
when the gate transitions to the low state. This delay
increases the peak current limit by (VTRANS)(tDELAY)/LPRI.
Setting The Target Output Voltage
The parameters that determine the target output voltage
are the resistors RVOUT and RBG, the turns ratio of the
transformer (N), and the voltage drop across the output
diode (VDIODE). The target output voltage is set according
to the following equation:
⎛
⎞
R
VOUT = ⎜ 1 . 24V • VOUT • N⎟ – VDIODE
RBG
⎝
⎠
Use at least 1% tolerance resistors for RVOUT and RBG.
Choosing large value resistors for RBG decreases the
amount of current that charges the parasitic internal
capacitances and degrades the response time of the VOUT
comparator. This may result in overcharging of the output
capacitor. The maximum recommended value for RBG is
2.5k for typical applications.
When high primary currents are used, a voltage spike
can prematurely trip the output voltage comparator. A
33pF to 100pF capacitor in parallel with RBG is sufficient to
filter this spike for most applications. Always check that
the voltage waveform on RBG does not overshoot and that
it reaches a plateau at maximum VOUT.
Discontinuous Mode Detection
The RDCM resistor stands off voltage transients on the
drain node. A 43k, 5% resistor is recommended for 300V
applications. Higher output voltages will require a larger
resistor.
In order for the LT3750 to properly detect discontinuous
mode and start a new charge cycle, the reflected voltage to
the primary winding must exceed the discontinuous mode
comparator threshold which is nominally 36mV. The
worst-case condition occurs when VOUT is shorted to
ground. When this occurs, the reflected voltage is simply
the diode forward voltage drop divided by N.
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Board Layout
The high voltage operation of the the LT3750 demands
careful attention to board layout. Observe the following
points:
1. Minimize the area of the high voltage end of the secondary winding.
3. Keep the electrical path formed by C1, the primary of T1
and drain of the NMOS as small as possible. Increasing
the size of this path effectively increases the leakage
inductance of T1 resulting in an overvoltage condition
on the drain of the NMOS.
2. Provide sufficient spacing for all high voltage nodes
(NMOS drain, VOUT and the secondary winding of the
transformer) in order to meet breakdown voltage
requirements.
RBG
CHARGE
1
10
2
9
3
VCC
CIN
LT3750
T1
1:N
PRIMARY
RDONE
DOUT
CPRI
8
4
7
5
6
RDCM
•
•
SECONDARY
CTRANS
VTRANS
+
COUT
RVOUT
RSENSE
M1
3750 F04
Figure 4. Recommended Board Layout
(Not to Scale)
3750fa
11
LT3750
U
TYPICAL APPLICATIO S
300V, 3A Capacitor Charger
T1
1:10
VTRANS
C3
56µF
C2
10µF
VCC
12V
VTRANS
RVOUT
VCC
C1
10µF
100k
4, 5
D1
VOUT
300V
1
•
•
60.4k 6, 7
+
C4
100µF
10
43k
DONE
RDCM
LT3750
OFF ON
CHARGE
GATE
M1
SOURCE
GND
RBG
25mΩ
2.49k
33pF
3750 TA02a
C1: 25V X5R OR X7R CERAMIC CAPACITOR
C2: 25V X5R OR X7R CERAMIC CAPACITOR
C3: 25V SANYO OS-CON 25SVP56M
C4: 330V RUBYCON PHOTOFLASH CAPACITOR
D1: DIODES INC. MURS160
M1: PHILIPS PHT6NQ10T
T1: TDK DCT15EFD-U44S003 FLYBACK TRANSFORMER
3A Charging Efficiency
3A Charge Time
100
300
VTRANS = 18V
VTRANS = 18V
NMOS DRAIN
CURRENT
1A/DIV
250
90
VTRANS = 6V
VTRANS = 12V
200
VTRANS = 6V
80
VOUT (V)
EFFICIENCY (%)
Typical Switching Waveforms
70
VTRANS = 12V
NMOS DRAIN
VOLTAGE
20V/DIV
150
5µs/DIV
100
60
50
3750 TA02d
50
0
0
50
100
150
200
VOUT (V)
250
300
3750 TA02b
0
0.2
0.4
0.6
TIME (SECONDS)
0.8
1.0
3750 TA02c
3750fa
12
LT3750
U
TYPICAL APPLICATIO S
300V, 6A Capacitor Charger
T1
1:10
VTRANS
C3
56µF
×2
C2
10µF
VCC
12V
VCC
C1
10µF
VTRANS
RVOUT
3, 4, 5, 6
VOUT
300V
1
•
•
60.4k 7, 8, 9, 10
100k
D1
+
C4
100µF
12
43k
DONE
RDCM
LT3750
CHARGE
OFF ON
GATE
M1
SOURCE
GND
RBG
12mΩ
2.49k
100pF
3750 TA03a
C1: 25V X5R OR X7R CERAMIC CAPACITOR
C2: 25V X5R OR X7R CERAMIC CAPACITOR
C3: 25V SANYO OS-CON 25SVP56M
C4: 330V RUBYCON PHOTOFLASH CAPACITOR
D1: DIODES INC. MURS160
M1: PHILIPS PHT6NQ10T
T1: TDK DCT20EFD-U32S003 FLYBACK TRANSFORMER
6A Charging Efficiency
6A Charge Time
Typical Switching Waveforms
300
100
VTRANS = 18V
VTRANS = 18V
VTRANS = 6V
VTRANS = 12V
80
200
VOUT (V)
EFFICIENCY (%)
90
NMOS DRAIN
CURRENT
2A/DIV
250
VTRANS = 6V
VTRANS = 12V
NMOS DRAIN
VOLTAGE
20V/DIV
150
70
100
60
50
5µs/DIV
3750 TA03d
50
0
0
50
100
150
200
VOUT (V)
250
300
3750 TA03b
0
0.1
0.2
0.3
TIME (SECONDS)
0.4
0.5
3750 TA03c
3750fa
13
LT3750
U
TYPICAL APPLICATIO S
300V, 9A Capacitor Charger
T1
1:10
VTRANS
C3
56µF
×3
C2
10µF
VCC
12V
VCC
C1
10µF
3, 4, 5, 6
•
60.4k 7, 8, 9, 10
100k
VOUT
300V
1
•
VTRANS
RVOUT
D1
+
C4
100µF
12
43k
DONE
RDCM
LT3750
CHARGE
OFF ON
GATE
M1
SOURCE
GND
RBG
8mΩ
2.49k
100pF
3750 TA04a
C1: 25V X5R OR X7R CERAMIC CAPACITOR
C2: 25V X5R OR X7R CERAMIC CAPACITOR
C3: 25V SANYO OS-CON 25SVP56M
C4: 330V RUBYCON PHOTOFLASH CAPACITOR
D1: DIODES INC. MURS160
M1: PHILIPS PHM2INQ15T
T1: TDK DCT20EFD-U32S003 FLYBACK TRANSFORMER
9A Charging Efficiency
9A Charge Time
100
Typical Switching Waveforms
300
VTRANS = 18V
VTRANS = 18V
VTRANS = 6V
200
VTRANS = 12V
VOUT (V)
EFFICIENCY (%)
90
VTRANS = 6V
80
NMOS DRAIN
CURRENT
4A/DIV
250
VTRANS = 12V
NMOS DRAIN
VOLTAGE
20V/DIV
150
5µs/DIV
100
3750 TA04d
70
50
60
0
50
100
150
200
VOUT (V)
250
300
3750 TA04b
0
0
0.05
0.10 0.15 0.20
TIME (SECONDS)
0.25
0.30
3750 TA04c
3750fa
14
LT3750
U
PACKAGE DESCRIPTIO
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.497 ± 0.076
(.0196 ± .003)
REF
10 9 8 7 6
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0° – 6° TYP
GAUGE PLANE
1 2 3 4 5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.127 ± 0.076
(.005 ± .003)
MSOP (MS) 0603
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
3750fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT3750
U
TYPICAL APPLICATIO
300V, 9A, 2.5mF Capacitor Charger
T1
1:10
VTRANS
C2
10µF
VCC
12V
VCC
C1
10µF
VTRANS
RVOUT
C3 4, 5
56µF
×3
60.4k
100k
D1
VOUT
300V
1
•
•
6, 7
+
C4
2.5mF
10
43k
DONE
RDCM
LT3750
OFF ON
CHARGE
GATE
M1
SOURCE
GND
RBG
8mΩ
2.49k
100pF
3750 TA05a
C1, C2: 25V X5R OR X7R CERAMIC CAPACITOR
C3: 25V SANYO OS-CON 25SVP56M
C4: CORNELL DUBILIER 7P252V360N082
D1: DIODES INC. MURS160
M1: PHILIPS PHM21NQ15T
T1: MIDCOM 32052 FLYBACK TRANSFORMER
Efficiency
Charge Time
100
300
95
VTRANS = 18V
250
VTRANS = 12V
90
200
VTRANS = 12V
VOUT (V)
EFFICIENCY (%)
VTRANS = 18V
85
VTRANS = 6V
VTRANS = 6V
150
80
100
75
50
70
0
50
100
150
200
VOUT (V)
250
0
300
0
3750 TA05b
1
2
3
4
5
TIME (SECONDS)
6
7
8
3750 TA05c
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3420/LT3420-1
1.4A/1A, Photoflash Capacitor Charger with
Automatic Top-Off
Charges 220µF to 320V in 3.7 Seconds from 5V, VIN: 2.2V to 16V,
ISD < 1µA, 10-Lead MS Package
LT3468/LT3468-1
LT3468-2
1.4A, 1A, 0.7A, Photoflash Capacitor Charger
VIN: 2.5V to 16V, Charge Time: 4.6 Seconds for LT3468 (0V to 320V, 100µF,
VIN = 3.6V), ISD < 1µA, ThinSOT Package
LT3484-0/LT3484-1
LT3484-2
1.4A, 0.7A, 1A Photoflash Capacitor Charger
VIN: 1.8V to 16V, Charge Time: 4.6 Seconds for LT3484-0
(0V to 320V, 100µF, VIN = 3.6V), ISD < 1µA, 2mm × 3mm 6-Lead
DFN Package
LT3485-0/LT3485-1
LT3485-2/LT3485-3
1.4A, 0.7A, 1A, 2A Photoflash Capacitor Charger
with Output Voltage Monitor and Integrated IGBT
VIN: 1.8V to 10V, Charge Time: 3.7 Seconds for LT3485-0
(0V to 320V, 100µF, VIN = 3.6V), ISD < 1µA, 3mm × 3mm 10-Lead DFN
Driver
3750fa
16
Linear Technology Corporation
LT 0106 REV A • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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